Test site: Biological characteristics of Corynebacterium diphtheriae. Analysis: Corynebacterium diphtheriae is a gram-positive bacterium with slender and slightly curved cells and one or both ends expanded. No capsule, no spore, no flagella, no sterile hair. Bacteria are arranged in L, V, Y shapes and irregular fences. At one end or both ends of the bacteria, there are heavily stained particles, which are unevenly colored with the bacteria, so it is called metachromatic granules.